Conformationally constrained fatty acid ethanolamides as cannabinoid and vanilloid receptor probes

To investigate if certain acylethanolamides bind to both cannabinoid (CB₁ and CB₂) and vanilloid TRPV1 receptors because of their conformational flexibility, we introduced a methylene lock on their ethanolamine "head", thereby generating a cyclopropane ring with two stereogenic centers and chiral cis/trans diastereomers with different topology of presentation to binding sites. After resolution by chiral-phase HPLC, diastereoand enantiopure arachidonoyl-, oleoyl-, and palmitoylcyclopropanolamides were tested in assays of CB₁, CB ₂, and TRPV1 activity. Diastereodifferentiation between pairs of cis-trans isomers was observed only for TRPV1 activity, with poor enantiodifferentiation. Methylenation introduced (i) CB₁ receptor affinity in oleoylethanolamide while increasing in a diastereoselective way its activity at TRPV1 and (ii) strong diastereoselective activity at TRPV1, but not cannabinoid, receptors in the otherwise inactive palmitoylethanolamide. These results show that the N-alkyl group of acylethanolamides has a different role in their interaction with cannabinoid and vanilloid receptors and that acylcyclopropanolamides qualify as CB₁/TRPV1 "hybrids" of potential therapeutic utility.